Crystallization and preliminary crystallographic study of the outer-membrane lipoprotein receptor LolB, a member of the lipoprotein localization factors.

The Lol system mediates the translocation of the water-insoluble outer-membrane lipoprotein across the periplasm of Gram-negative bacteria depending on the sorting signal. The outer-membrane lipoprotein receptor LolB (21.2 kDa) is a member of the Lol system. A soluble mutant of LolB (mLolB) from Escherichia coli was crystallized in two forms. Monoclinic crystals diffract X-rays to 1.9 A resolution and belong to space group P2(1), with unit-cell parameters a = 37.2, b = 112.4, c = 47.8 A, beta = 111.4 degrees. The V(M) value is most likely to be 2.2 A(3) Da(-1), assuming the presence of two molecules in the asymmetric unit. Hexagonal crystals diffract X-rays to 2.2 A resolution and belong to space group P6(3)22, with unit-cell parameters a = b = 71.4, c = 133.9 A. The V(M) value is determined as 2.3 A(3) Da(-1), assuming a single molecule in the asymmetric unit. A four-wavelength data set was collected from a monoclinic crystal of selenomethionylated mLolB in order to perform MAD phasing. The quality of the initial electron-density map was sufficient to build a molecular model.